CHAPTER 6: COMBINING INDICATORS
6.1 Introduction  combinations to provide corroborating
evidence and a consistent view of land
Single indicators give singular items of degradation
evidence for land degradation or its impact.  methods to bring individual indicators
They are susceptible to error, misinterpretation together for comparative and overall
and chance. Especially in the case of field assessment, including how to search for a
assessment where many of the measurements suite of indicators and how to develop a
can only be described as 'rough-and-ready', the semi-quantitative procedure for getting an
use of only one indicator – say, a tree mound – overall picture.
to conclude definitively that land degradation
has occurred is problematic. It renders the field However, before considering how indicator
assessor open to criticism that much is being combinations can be constructed, why are they
made of a little. Therefore, this chapter really necessary in all but the simplest of
addresses how, by combining indicators, more situations?
robust conclusions can be entertained, even to
the extent that quite different types of measure
may be placed alongside each other to obtain a 6.2 Why Single Indicators are Often
fuller understanding as to whether land Insufficient
degradation is happening.
An example is used here to illustrate how
This publication has throughout single indicators, especially when used with
promoted the use of two or little reference to the farmer, may give
more indicators in combination, erroneous conclusions.
preferably with the active input
of farmer experience. Just as a Figure 6.1: Sketch of Bench Terraces
three-stranded rope is far
stronger than the sum of the
strengths of its individual
strands, so is an assessment of land degradation
based upon the combination of indicators that
all trend towards the same conclusion. While
each indicator has its own attributes and
applications, several indicators together can
piece together a far more comprehensive and
consistent picture. Similarly, if indicators
disagree in general trends, then the field
assessor is led to further investigation to
resolve the disparities. Disagreement in what Accumulations of sediment behind barriers are
the indicator suggests is one of the most a useful indication that soil movement has
powerful ways of picking up the difference in taken place in the field, and that, if it were not
perspectives of the land user and the field for the barrier, soil would have been
professional. irrecoverably lost. A typical example is shown
in Figure 6.1, where the sediment trapped
Three particular areas of combining indicators (shaded) by the constructed riser of the bench
are highlighted here: terrace can be measured to give an assessment
 combinations to show both the process of the minimum amount of soil that has been
and likely cause of land degradation lost from the bench. The assumption here is
through time that the material trapped has been eroded from
68
the bench because of the land use and slope of called 'plough erosion', that is, soil moved
the bench. Is this necessarily so? down by the action of cultivation.
Therefore, we have a situation where erosion
has been 'encouraged' by the farmer. Is this
land degradation? The field assessor must
decide. However, it is useful to view the
supposed eroded soil through the eyes of the
farmer because:
 here is a useful site to get rid of weeds and
other 'rubbish' – indeed, the fence line in
the local language is called 'rubbish-things
fence';
 after a few seasons when the benches are
formed, the soil close to the fence is
relatively rich in organic matter as well as
being deep; hence the more valuable and
demanding crops are planted here;
 meanwhile, the farmer harvests poles of
Gliricidia for sale or use as bean-poles,
while the leaves are left on the surface soil
for a nitrogen-rich mulch;
Figure 6.2: Farmer planting Gliricidia
 after six or seven years, when the
Fence, Sri Lanka Gliricidia starts to lose its vigour, the
farmer uproots the fence line, and plants
high value crops in the accumulated rich
In Sri Lanka, these types of bench terrace are soil;
common in the steep hill lands where a living  at the same time, a new Gliricidia fence
plant is used to support the riser and maintain line is constructed mid-way across the old
the benches. (See Section 7 for a fuller case bench ….. and so the process continues.
study of this type of conservation). It is
instructive to follow through with farmers how Only with the farmer fully participating can
they construct the benches and what they think this story of soil movement and farm
of the soil that is trapped behind the riser. The production be told. So, again, is this land
risers themselves usually consist of planted degradation? First, there is positive
lines of a fast growing leguminous tree, encouragement by the farmer for soil to move
Gliricidia sepium. A farmer will cultivate the to fill in the upslope side of the fence.
field and then plant a new line of G. sepium Secondly, there are interesting management
sticks across the slope. At this stage there are and production opportunities opened up by the
no benches. Progressively, over a few seasons, accumulation of soil. Thirdly, the farmer sees
the farmer then: the accumulation as a longer-term production
 manages the Gliricidia sticks so that they opportunity, while a new fence line in another
'strike' and commence growing into trees; part of the field is established. There has been a
 along the line, the farmer places sticks to real and measurable movement of soil. But
form a more permanent barrier; weeds are humans have done most of it for very specific
also placed here, as it is a convenient close reasons related to their livelihoods. The soil
place and does not interfere with crop movement will have contributed to the
activities between the lines of sticks; deterioration of part of the slope for some six
 with the hoe, the farmer scrapes soil to seven years. But the farmers gain sufficient
downslope to cover the weed-fill and form capital assets to implement a further cycle of
benches; some soil is washed down soil restoration with the new fence lines, while
naturally by rainwash but most is what is fully utilising the 'eroded' soil for their benefit.
69
The answer as process comes to have an impact on
to whether this production.
is land
degradation Take the case of a flat-cultivated field where
must, therefore, observation and measurement of 'armour layer'
depend upon has shown that active current erosion is taking
the perspective place under an extremely poor cover of maize.
through which The coarse stones accumulating on the surface
the judgement are evidence, not only of total erosion, but also
is made. It is that there is substantial selective removal of
like the alternative views on a glass of milk fine particles. However, the impact of this
that has been half-consumed. The optimist will selective removal and how the erosion is
say, "Good – it is still half-full"; the pessimist causing a reduction in plant vigour (and
will complain, "It is half-empty". The optimist presumably also of yield) have yet to be
will be the farmer. In field surveys in Sri discovered.
Lanka, not a single farmer equated the soil
movement with soil erosion – they saw it as
part of the natural production cycle on steep
hill slopes. The pessimist is the professional –
soil is moving downslope, and what is worse is
that farmers are even accelerating the process
with their cultivation techniques!
The single indicator, with little reference to the
farmer, could in this instance (and many
others) present a simplistic and erroneous –
from the farmer-perspective – understanding of
the status of land degradation. The fuller Figure 6.3: Field Showing Poor Maize Growth
picture is only available by, for example,
examining plant growth on the eroded soil; the Examination of the growing maize plants and
use of the Gliricidia branches and leaves; and, other field indicators for:
crucially, by observing what is done and  nutrient deficiency symptoms – to
talking with the farmer as to why things are discover if there is a causative effect
done in this way. The single biophysical through plant nutrient limitations:
indicator needs supplementation by all these yellowing, chlorotic leaves of the maize
other observations before land degradation can  differential crop growth characteristics
even be considered as having occurred. between eroded and uneroded conditions
to determine if it is the erosion that is
reducing yield, and by how much: a
6.3 Assessment of Both Process and Cause nearby site cultivated for only a few years
has double the plant density and much
The example above has already illustrated how larger plants
process and cause can be discerned in a  any sediments entrapped in field ditches,
complex field system of bench terraces. The or hollows, for evidence of the degree of
field observation indicated that there had been enrichment: some coarse sands in a field
a 'process' of erosion; the further enquiry found ditch in the middle of the field; and some
the 'cause', deliberate ploughing and very fine clays and rich humus in a puddle
entrapment of sediment by the farmer. Just as at the bottom of the field …..
powerful conclusions may also be drawn in all add to the understanding of how the obvious
simpler situations where two indicators process of erosion under a poor standing crop
essentially agree but one is a measure of the affects current and future production from the
process and the other a measure of how the field. In this case, the indicators are all in
70
agreement in the sense that they all point to a
consistent process (erosion-induced loss in soil
productivity) and cause (selective removal of
organic matter and clays and consequent
nitrogen deficiencies for the maize)
Piecing together the separate strands of field
evidence is one of the most exciting aspects of
field assessment of land degradation, because
they enable far more to be gained than with
classical reductionist methods, where only the
knowledge of a process may be gained. Here, Figure 6.4: Maize Planted Up and Down Slope
an interesting inter-weaving of process, cause
and effect may be gained, provided that the are discontinuous and some contain the
field observer is alert to the signs and is willing remains of organic matter. Closer field
to put together evidence from a variety of inspection shows there is an average length
sources. of rill of 4 m; cross-sections average 5 cm
wide by 5 cm deep; and the average
contributing catchment to each rill is one
metre wide (the row width) and 5 metres
6.4 Triangulation – Gaining a Robust View of
long. So each rill has a space volume of
Land Degradation
0.01 m3 per 5 m2 of field. The organic
Mention has already been made in Section 1.3 matter seems to come from grasses and
that farmer-perspective, field assessments of small herbs. The farmer observes that these
land degradation may be criticised by some as rills occur every year, and he finds them
being less reliable than standard measurement. useful as narrow paths to get into his field
The principal ways to overcome any possible for weeding, as well as places in which to
lack of precision are a) to take as many put the weeds.
individual assessments as possible, and b) to  The soil has a significant number of coarse
examine the general trends of several different quartz fragments some 2-3 mm across.
types of measure to see if they are in Between the rows of growing maize, these
agreement. This second means is known as fragments provide the capping material for
triangulation, the gaining of a consensus view pedestals in-field. A sample of pedestals
of overall trends from different types of gives a mean height of 2.5mm. The farmer
assessment. confirms he last weeded with a hoe three
weeks previously.
Example of triangulation using nine indicators  There are several trees within and around
the field that have been left for shade after a
Take the example of a degraded catchment that hot day's weeding and for their wild fruit.
has been largely deforested in order to plant Tree mounds are apparent, indicating that
annual crops of maize and beans with no the surface of the soil in the field has
obvious dedicated measures of soil and water lowered because presumably topsoil has
conservation. There are some trees and field- been washed off since the field was opened
plot boundaries. The maize is planted in rows for cultivation. According to the farmer this
up-and-down the slope. It is now two months was 20 years ago. The mounds average 15
since the rains started. A reconnaissance field cm in height above the surrounding soil
survey with the farmer has revealed the surface, though there is some considerable
following, with some preliminary variation between top (higher – up to 30
measurements: cm) and bottom (very little) of field.
 In the furrows between the rows of maize,  While at the downslope end of the field,
rainwash has concentrated and formed rills our observer notes that there are boundary
within the planted beds of maize. These rills accumulations of soil that average 10 cm
71
deep against the grass path between this significant, with the upper parts generally
field and the one immediately downslope. poorest. Germination rate as evidenced by
Examining the accumulations more closely, plant population density, however, seems to
a rough calculation indicates an average be relatively uniform.
volume accumulation of 0.01 m3 per metre  Maize nutrient deficiencies are also evident
length of boundary. Since the field is 10 in the leaves of the growing crop. At the
metres long, the contributing area is 10 m2 , top of the plot, plants are stunted and
and the sediment therefore amounts to 10 yellow-looking. Towards the lower and
m3 per hectare. The farmer interjects at this middle parts of the field some of the plants
stage that he only subdivided the field the have a purplish colour on new leaves, but
previous year and sold the downslope part those plants growing in the sediment
to his neighbour, and so the path has only accumulation along the boundary are
been there for just over a year. sturdy, vigorous and deep green in colour.
 Walking then to the middle of the field, the  Then, finally, our observer walks with the
observer notes that the farmer has farmer to the lower boundary of the field to
constructed a small drainage ditch across see if there is any evidence of land
the slope to protect the lower field from degradation processes outside the
runoff during heavy storms. There is immediate field. There, in a hollow is some
sediment in the within-field drainage ditch, fine mud and organic material, obviously
amounting on average to 0.001 m3 per collected after the last rainstorm from soil
metre length of drain. The sediment is that had been completely washed out from
mainly medium to coarse sand – the fines the field. Here the enrichment of sediment
have apparently been washed completely in the downstream hollow can determine
out of the field. Since each metre of drain the quality of the material that has been
has a contributing area of 5 m2, this entirely lost from the field. The clay and
amounts to 2 m3 of sediment per hectare. organic matter amount to 100 percent of the
The farmer tells our observer that he has to sediment in the hollow, whereas in the field
dig this drain out each year as it fills up, clay is less than 20 percent. This indicates
and redistribute the sediment across the an approximate enrichment of the eroded
field, or else the drain will not work. sediment by a factor 5:1
 While at the top of the field, our observer
digs a small hole to examine the soil. Soil In this example, the nine different types of
depth is very shallow, averaging only about measure all indicate that processes of land
25 cm, with little differentiation in colour degradation are operating. They all show
(a light yellow-brown) between subsoil and different parts or different aspects of
topsoil. The farmer says he is getting degradation processes that have been set in
worried about this part of the field and has train from when the land was originally opened
noticed the soil getting lighter and sandier. up for cultivation. So there is a general
When he started cultivating there 20 years consistency in trends, but the evidence is
ago, it was 50 cm deep with 10-cm rich complex. Our field assessor can certainly
topsoil. At this stage, the farmer gets his conclude that there has been degradation and it
hoe out and shows the field assessor how is having a significant (and increasing) impact
he cultivates: standing facing uphill, the on crop growth in parts of the field. However,
farmer progressively brings soil downslope the simple calculations of the absolute levels of
– this is an immediate explanation for the soil erosion from pedestals, rills, tree mounds,
lack of soil depth here at the top of the boundary wall accumulations and sediment in
field. ditches do not agree. This is unsurprising
 Walking into the maize crop with the because they represent different spatial and
farmer, the observer notes that some parts temporal scales, as well as different parts of the
of the field seem to be doing well, while overall process of land degradation. Some
other parts have suffered stunted growth. measures give a view of the erosion for the last
Within-field variation of crop growth is three weeks (pedestals). One shows what has
72
happened since the field was last ploughed 2 or (tree mounds) to half the field (sediment in
more months previously (rills); one from the drainage ditch) and the whole field (Boundary
last year (boundary wall accumulation); right accumulations), and even the whole slope
up to one which integrates the situation of the (enrichment in downslope hollow). So, it is
field and its land use for the last 20 years (tree necessary to examine the different items more
mounds). The spatial scales vary from being closely (Table 6.1) and piece together a
representative of a single point on the slope comprehensive picture.
73
Table 6.1: Example – Field of Maize and Nine Indicators
(#Sub-Section) Quantitative Interpretation
Indicator Assessment
(#4.1) Rills Rill erosion of This rill erosion has occurred in the current season: probably most of it in very early season
within planted 26 t/ha since storms before the crop has germinated. Rills act to channel excess water and sediment – so the
beds of maize the last field soil loss represented by the volume of the rill will only be a fraction of total soil loss from the
(0.01 m3 per 5 cultivation to field [this observation is corroborated by the pedestals, suggesting an approximately 4:1 ratio
m2 of field) prepare between sheet soil loss and rills – about right for most fields]. Now, with weeds placed in the
ground prior rills and the better cover from the maize, there will be little more additional rilling – maybe even
to planting 2 some sedimentation.
months ago
(#4.3) Pedestals Sheet erosion This is a significant removal of soil during the middle growth period of the maize, indicating
in-field. (2.5 of 32.5 t/ha in that the crop has given relatively poor cover to the soil. The erosion rate in the 3-4 weeks prior
mm high) the last 3 to weeding and after planting must have been just as high, if not higher, because of the poorer
weeks since vegetation cover then. The observer needs to enquire whether there were large rains then. If
weeding there were, then this suggests an annual sheet erosion rate of the order of 70-100 t/ha.
(#4.8) Tree Cumulative If distributed evenly over the 20 years, there would have been nearly 100 t/ha/yr sheet erosion in
mounds (15 cm sheet erosion this field. Erosion in the early years would likely have been less because the soil would have
high) of 1950 t/ha been in better condition. So this indicates a high long-term rate of erosion of 100 t/ha/yr since
over the last deforestation, and a current rate of erosion of possibly 120-150 t/ha/yr. These figures are slightly
20 years higher than those calculated from current sheet erosion (pedestal indicator) plus rill erosion –
(70-100 + 26). The assumption of lower soil loss in early years may be incorrect – ask the
farmer what was grown then and if the land had been kept bare or suffered major rainstorms.
(#4.9) 13 t/ha in the This is a new grass path created just over a year ago. The grass has intercepted sediment and
Boundary last year water from the field, and the accumulation has built up. But from these figures, it is apparent
accumulation that about 90% of the sediment has gone through the boundary, probably in the larger storms.
(10 m3 per Nevertheless, the boundary has succeeded in 'saving' 10% of the loss, including some fine
hectare) particles. Over time, the interceptive ability of this grassed path should get better, as the field
slope reduces by the accumulation and the grass becomes more vigorous. Additionally, the
deposited sediment will be fertile and so a better crop should grow - see next indicator
(#4.10) 2.6 t/ha since These sediments represent only the coarsest fraction of the soil that has moved across the upper
Sediment in preparation of part of the field slope. Field observation of its texture (see #5.4) suggests that this fraction is
within-field land 2 months only 10% of the whole soil. Hence, this is evidence that a minimum of 26 t/ha of soil was eroded
drainage ditch ago to produce this material. It is a minimum because some of this same sand fraction may have
(0.001 m3 per remained in the field (and not caught in the drain), and some may have been washed out of the
metre length of drain in very large storms. Because erosion selectively removes the fine particles, the actual
drain) amount of soil eroded in the 2 months must have been much larger than the 26 t/ha calculation,
which is not inconsistent with the 70-100 t/ha from pedestals indicator.
(#4.13) Soil Sheet erosion This reduction in soil depth, based upon farmer estimates as to original soil depth (but capable
depth (25 cm loss of 25 cm of corroboration by the field assessor on an adjacent site at same position on slope), occurred at
deep at top of in 20 years; or the top of the field where maximum erosion has happened. However, some of this loss is
field; 50+ cm at about 160 'cultivation erosion': i.e. the farmer has dug soil downslope. The field assessor needs to
bottom) t/ha/yr determine to what extent this direct intervention in land degradation by the farmer should be
included. As there has been deposition at the base of the field (hence erosion is zero there), 160
t/ha/yr would give an average sheet erosion over the field of 80 t/ha/yr since the field was
opened up.
(#5.1 & #5.2) No Observations are consistent with soil having moved from the top part of the field to the bottom.
Within-field quantitative This indicator is a measure of impact of land degradation, showing that crop growth on the
variation of assessment 'eroded' soil at the top is significantly poorer than lower down the field where soil removal has
crop growth. possible been less, and very much poorer than on the lower boundary where there has been some
deposition
(#5.3) Maize No The stunted, yellow plants at the top of the field are clear evidence of both poor growth because
nutrient quantitative of lack of soil rooting volume and lack of sufficient nutrients and water. In that germination (as
deficiencies assessment evidenced by plant density) was relatively uniform, the restricted growth only became evident
possible once the plant had higher demands for nutrients and water. The purplish colours of the leaves in
mid-slope is evidence of phosphorus deficiency. Phosphates are easily washed downslope by
erosion; some may have accumulated in the deposited sediment (hence the good growth there)
but most have been taken off in solution. The deep green of the plants at the lower end of the
field indicates good water and nitrogen supply – much of this is accumulated from the higher
parts of the field.
(#4.11 & #5.4) Five times as The hollow will have trapped a representative sample of water and sediment exiting from the
Enrichment of much clay in whole field. As the puddle in the hollow dried out, the clays and other fine material (e.g. humus)
sediment in a the hollow settles out. The 5:1 enrichment indicates that the impact of land degradation processes is a very
downstream than in the significant influence on the fertility of the field. Most of the sands are redistributed in the field,
hollow. (5:1) soil from but the main fertile fractions are almost (except for a small amount trapped behind the grass path
which it came. boundary) completely removed from the field. Future production will be affected far more than
in proportion to total amounts of soil lost – the factor 5 suggests a crash in yields after only a
few more years unless remedial measures are taken.
74
The comprehensive picture have an open mind,
observant eyes, and
In the above example, triangulation has the qualities of a
provided the field assessor with powerful detective.
conclusions that land degradation is currently
active. Also, there is a substantial current effect It is difficult to
on production and the loss of fine material is provide specific
potentially serious to future yields. Previous guidance for all situations – there are many
land use probably also saw degradation but at a permutations of possible land degradation and
lower rate. land use conditions, and hence many possible
interpretations. Therefore, in the following two
The evidence all indicates that the major sub-sections, suggestions are made for a) the
influence on land degradation has been the approach to adopt in the field, and b) how to
opening up of this piece of land to annual put the indicators together in a semi-
arable crops without any form of protection or quantitative form for initial inspection.
conservation, other than the field drainage ditch
and the new grassed path acting as a lower field A checklist for the field
boundary. Overall current sheet erosion rates
are at least 100 t/ha/yr, with possibly another It is important to make a careful reconnaissance
25% addition to account for rilling. Only a of the field site to note all the pieces of
small percentage (c. 20%) of this sediment is evidence of both land degradation processes
caught in-field – 10% of coarse sands in the and their impact. The following checklist is for
drainage ditch and 10% of more representative general guidance only. Like any good
fractions of the whole soil against the field detective, the field assessor must follow-up any
boundary. Erosion-induced loss in productivity interesting leads, especially those initiated by
is also serious, through a large reduction (50%) comments from the farmer.
in plant-rooting volume at the top of the slope,
which affects nutrient and water supply to 1. Map out the field slope as a sketch, noting
growing plants. The erosion-induced limitation the position of any obvious features such as
in mid-field is a reduction below critical gullies, rills, tree mounds, boundary walls.
threshold of available (soluble) phosphorus. At 2. Obtain the history of land use: when the
least two-thirds of the field is affected by plot of land started to be used, crops grown,
serious land degradation, while the lower third any change in land use, subdivisions of the
has gained somewhat. However, still a very land, and similar important events that
large percentage of fine particles and organic could have a bearing on land degradation.
matter has been lost entirely from the field. (These events should later be set alongside
the field measurements to ascertain whether
they correspond with observations.)
6.5 Guidelines for Combining Indicators 3. Determine any significant events:
landslides, exceptionally heavy storms and
Finally, in this chapter, some guidance is given soil wash, dates when trees were cut down.
as to how to approach the challenge of 4. Note any particular farming techniques that
combining indicators. It is a challenge because may have implications for land degradation
studies in land degradation have been (e.g. ridging practices across/down the
bedevilled by reductionism. Approaches to slope; hand cultivation downslope)
measurement have usually been satisfied with 5. Then, with the map in 1. Above, and
single sets of observations rather than the preferably accompanied by the farmer, go
approach advocated here. Yet, the example through the indicators of the processes of
above demonstrates that a comprehensive view land degradation:
of the effect of the history of land use can be  soil losses from single places (e.g. tree
gained if the pieces of information are set side- mounds; pedestals; soil depth)
by-side. The field assessor must, above all,
75
 soil losses from small parts of the field that someone may take these absolute figures
(e.g. rills, armour layer) (as has often happened) to use them as precise
 soil losses from large parts or the whole evidence of the level of degradation, then it
of the field (e.g. gullies; differences in may well be better not to give the figures in the
soil depth between degraded field and first place. The alternative is a semi-
non-degraded; or averages over the quantitative assessment.
field of previous items such as tree
mounds) 'Erosion Hazard Ratings - EHRs' (see
 sediment accumulations and their Bibliography) are one example. The factors of
enrichment/texture within the field (e.g. erosion – slope, soil type, vegetation cover, and
drainage ditches; against an in-field rainfall – are rated on a numeric scale, usually
tree) one to five in severity of likelihood to cause
 sediment accumulations and their erosion. Then these individual factor ratings are
enrichment/texture at the base of the combined, either through a scoring system or
field (e.g. boundary accumulations) through a simple model, to give an overall
 sediment accumulations and their hazard rating. This is not an actual measure of
enrichment/texture outside the field land degradation, but a prediction of potential
(e.g. clay enrichment in hollows) land degradation according to the
6. Then, with the farmer (most important this environmental factors that encourage it. Such
time), determine the indicators of the assessments have been widely used for broad-
impact of land degradation: scale planning purposes. They are simple to
 observation of current plant growth develop and easy to visualise since the results
(e.g. within-field differences) are usually presented in the form of a map.
 actual measurements of different sizes EHRs are not, however, particularly useful at
of plants the detailed field level, or for developing a
 list known nutrient deficiencies farmer-perspective approach.
observed
 estimate, with farmer, likely yields from
different parts of the field
 obtain historical yields, and
observations on how plant growth has
changed.
7. Compile a comprehensive table of
indicators and results, looking for trends,
consistency and areas where there is broad
agreement in the scale of degradation.
8. Return to the farmer with your account of
the comprehensive picture, and get his/her
evaluation of your diagnosis.
A semi-quantitative assessment
Figure 6.5: Extract from Erosion Hazard
Assessment so far by combining indicators has Assessment for Zimbabwe
attempted to use absolute (scale) levels of land
degradation, such as tonnes soil per hectare. Instead, Malcolm Douglas in his Guidelines for
With the approximate nature of the techniques the Monitoring and Evaluation of Better Land
of assessment, this can be misleading unless Husbandry (see Bibliography) has suggested
careful precautions ('health warnings') are simple scoring techniques for seriousness of
taken. To say that exactly 126 t/ha/yr of soil simple indicators of land degradation (and
loss has occurred is folly, implying that it was conservation effectiveness). The reader is
more than 125 and less than 127. This degree referred to this 27-page publication for more
of exactitude is unjustified. If it is suspected details. However, it is perfectly appropriate to
76
Table 6.2: Sheet Erosion
Ranking Degree Description
X Not apparent No obvious signs of sheet erosion, but evidence of minor sheet erosion
may have been masked, for instance by tillage.
0 No sheet erosion No visual indicators of sheet erosion.
1 Slight Some visual evidence of the movement of topsoil particles downslope
through surface wash; no evidence of pedestal development' only a few
superficial roots exposed.
2 Moderate Clear signs of transportation and deposition of topsoil particles
downslope through surface wash; some pedestalling but individual
pedestals no more than 5cm high; some tree and crop roots exposed
within the topsoil; evidence of topsoil removal but no subsoil horizons
exposed.
3 Severe Clear evidence of the wholesale transportation and deposition of topsoil
particles downslope through surface wash; individual pedestals over
5cms high; extensive exposure of tree and crop roots; subsoil horizons
exposed at or close to the soil surface.
Table 6.3: Rill Erosion
Ranking Degree Description
0 No rill erosion No rills present within the field.
1 Slight A few shallow (< 100mm depth) rills affecting no more than 5% of the
surface area.
2 Moderate Presence of shallow to moderately deep rills (< 200mm depth) and/or
rills affecting up to 25% of the surface area.
3 Severe Presence of deep rills (up to 300mm depth) and/or rills affecting more
than 25% of the surface area.
develop one's own scoring system. Provided management, and b) soil management. The
that it is consistently used, it can be a good way 'effectiveness of conservation' is essentially a
of combining indicators to get a more composite view of both direct and indirect field
comprehensive view of land degradation. interventions by the land user. They include
how effectively crops protect the soil as well as
The tables above give two of the more the use of fertilizer and specific 'land
commonly used examples that combine husbandry' practices. Douglas' tables (adapted
observations of a number of separate below for these Guidelines) give a very useful
indicators. checklist of land user practices, as well as
bringing together a diverse number of farmer-
Douglas also suggests a three-point scale for activities into a comprehensive picture of the
the effectiveness of conservation for a) crop land degradation potential.
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Table 6.4: Crop Management Considerations
Crop management Conservation effective Conservation neutral Conservation negative
indicators Score 1 Score 2 Score 3
Change in percentage At least 40% cover of soil Little increase in ground Decrease in ground cover –
ground cover by the achieved by crop within 30 cover provided by crop remains below 40% for
growing crop days of the start of the rainy between fallow and most of the growing season
season growing crop
Intercropping/relay Cropping practices lead to No change in intercropping Cropping practices lead to
cropping improved ground cover or relay cropping practices reduction in ground cover
and/or increase in the ratio and/or decrease in the ratio
of legumes (N-fixing) to of legumes (N-fixing) to
non-legumes non-legumes
Spacing/planting density Ground cover improved No change in plant spacing Ground cover reduced
through closer crop spacing and density through wider crop spacing
and/or increased plant and/or decreased plant
density density
Improved seed/planting Adoption of improved No change in crop biomass Adoption of improved
material seed/planting material and ground cover seed/planting material
results in improved results in decreased
biomass production and biomass production and
better ground cover inferior ground cover
Fertilizer and/or organic Increase in fertilizer and/or No change in quantity of Decrease in fertilizer and/or
manures organic manures result in fertilizer and/or organic organic manures result in
more biomass production manures used for crop less biomass production
and better ground cover production and poorer ground cover
Crop residues Crop residues incorporated Not applicable Crop residues burnt or fed
into the soil or retained on to livestock
surface as protective mulch
To gain a composite view of the influence of largely effective in limiting the danger of land
crop management on land degradation, the six degradation and could help to rehabilitate
crop management indicators are scored 1 to 3. existing degraded land if implemented."
The minimum score is 6, indicating almost no Locally appropriate descriptions should be
contribution of crop management to land developed for ranges of scores, e.g.
degradation; the maximum is 18, indicating
extreme danger of rapid degradation. To bring 1.00 – 1.49 No land degradation danger; good
the composite view back to a 1-3 scoring scale, rehabilitation potential
1.50 – 1.99 Land degradation slight; good
divide the sum of the scores by the number of possibility of rehabilitation
indicators – in this case divide by 6. The 2.00 – 2.49 Moderate danger of land degradation –
'conservation effectiveness' can then be particular practices have specific
interpreted comparing different crop problems
management regimes in their likelihood to 2.50 – 3.00 Land degradation hazard high to very
high – all practices contribute to danger
contribute to land degradation. So, a total score
of 8 that gives an average score of 1.3 would be
interpreted as "crop management practices are
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Table 6.5: Soil Management Considerations
Crop Conservation effective Conservation neutral Conservation negative
management Score 1 Score 2 Score 3
indicators
Soil organic Interventions enhance soil organic Interventions only maintain soil Interventions fail to maintain
matter matter through, for example: organic matter levels by: soil organic matter levels:
a) Incorporation of crop residues; a) grazing livestock on crop a) removal or burning of all
b) application of at least 3 t/ha/yr residues in situ; crop residues
compost and/or animal manure b) application of compost b) no application of
c) application of at least 5 t/ha/yr and/or animal manure at compost and/or animal
of fresh green manure (e.g. rate below 3 t/ha/yr; manures;
Leucaena) c) application of fresh green c) no application of green
manure at rate below 5 manure – all biomass
t/ha/yr removed as fuel or fodder
Soil Interventions replace lost soil Traditional low input fertility Poor practices that continue
chemical nutrients through: management practices capable the depletion of soil nutrients
properties a) application of compost and/or of achieving low levels of through:
animal manure nutrient replenishment, through: a) continuous cultivation of
b) use of N-fixing species in crop a) short bush fallow cereal and root crops
rotations and intercropping, or b) tethered grazing of b) burning of crop residues
in N-rich green manures and livestock within farm plots c) little, if any, use of
hedgerows on crop residues and weeds compost, organic
c) enriched fallows c) retention of a few scattered manures or chemical
d) chemical fertilizer (as a trees on the croplands fertilizer
supplement, not a substitute for
organic manures)
Soil Interventions maintain and enhance Traditional low input practices Poor practices continue
physical topsoil structure through: neither combat nor promote physical degradation of the
properties a) minimum tillage physical degradation of the soil, soil, through:
b) planted pasture and enriched through: a) excessive tillage
fallows a) partial tillage b) continuous cultivation
c) incorporation of crop residues, b) short bush fallow c) no incorporation of
compost, animal manure, green c) retention of a few scattered organic matter
manures and tree litter trees on the croplands d) trampling by people and
livestock
For soil management considerations in the 6.6 Combining Indicators in the SRL
above table, a minimum score of 3 and a Approach
maximum of 9 is possible against the three
indicator variables. The same procedures apply Finally, in this chapter it is important to bring
to interpret these scores in terms of overall all the information together in a common
contribution to land degradation status. framework that puts the farmer-perspective to
the forefront. Chapter 3 and Table 3.1 gave a
Such tables should be adapted for the specific model for field assessment in terms of the
circumstances of each field and the different 'capital assets' of land users. These assets,
types of land use. Once developed for a local divided into natural, physical, human, social
area, they can provide excellent ratings to and financial capital, provide a useful means of
determine the specific danger of different types assembling all relevant items of information
of land use. Furthermore, they can be used to that have been identified. An abbreviated
assess proposed interventions alongside example based on a field of maize (Table 6.1)
existing practices to see if land degradation and a farmer (Fig 6.4) is provided in Table 6.6
status will be unduly changed. Such semi-
quantitative techniques, therefore, provide both
a current view and a predictive means to
monitor land degradation status.
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Table 6.6 Combining Indicators in the SRL Framework for a Field of Maize
– How Land Degradation is Affected
(See Sustainable Rural Livelihood Model in Table 3.1 and field data example in Table 6.1 with added information from
farmer interviews.)
Capital Asset Positive Effects of Change in Capital Negative Effects of Change in Capital
Natural Farmers have planted field boundaries, Deforestation has led to a substantial loss of
against which some soil accumulates (13 natural capital. The soil is now eroded; its water-
t/ha in the last year). As these boundaries are retaining properties are deficient; and the overall
enriched by planting of fruit trees and other stocks of biomass and plant diversity are much
economic species, their effectiveness in reduced. Biophysical indicators (Table 6.1)
accumulating natural capital will increase summarise the effects
Physical The farmer (Fig 6.4) has only a hoe for Poverty means little opportunity to accumulate
cultivation. This means he cannot extend his further means to manage the land resources. In
cultivation to larger areas. Instead, then, he effect the farmer is confined to cultivating simply
has to intensify land use on small plots and with no means of physical conservation.
use the benefits of multiple cropping to limit In addition, distance from markets and physical
the need for more tools and equipment. This infrastructure gives little opportunity to grow
is good for conservation, but hard for the high-value crops for sale.
farmer.
Human The farmer has a wealth of indigenous Old age and ill-health in the family (his wife is
knowledge, handed down from his father. very sick) means that farming practices must be
This includes the small drainage ditch across minimised if enough land is to be cultivated for
the field to protect from runoff. He tells us sufficient food to be grown. Human capital
about techniques he knows of composting limitations determine that the farmer's time-
and of building small terraces. These would horizon is short, and that there can be little
be excellent to control land degradation. But investment in the future – except those activities
in the pressure to grow the maximum which demand least labour (planting field
amount of maize for home consumption, boundary) and those that are essential for survival
much of this knowledge is not applied (cultivating maize).
Social Family and clan ties have enabled the farmer Family and clan ties also mean that part of the
to call on relatives and clansmen to get the crop has to be given over to other members of the
field ploughed early in the rainy season. This social network. To do this, the farmer has to take
has enabled timely planting and minimising off-farm employment to supplement income. He
the risk of erosion because of poor cannot then devote time to carrying out protective
vegetation cover. The maize crop is looking measures such as managing the runoff safely, and
good (Fig 6.4) mainly because of this to dealing with the maize nutrient deficiencies
communal effort in planting the seed on which manifest themselves in late season.
time.
Financial A rich uncle in the capital city remits enough No bullocks to pull the ridger. After negotiating
money for the farmer to buy an ox-drawn with a neighbour, he gets enough cash to hire the
ridger. Next year he can plough across the animals for ploughing next season. However, it is
slope, with planting undertaken on now late in the new season because the neighbour
conservation ridges that prevent further land wanted understandably to plough first. The
degradation…… but……. animals are exhausted, and the crop planting is a
failure. More land degradation.
Using the SRL framework in this way thus this sort of 'balance sheet' of how the farming
enables a balanced view of the complexities of situation changes the assets of a farmer to gain
real farming. Nothing is simple. Apparently a livelihood is built in a systematic way. Later
simple solutions such as added financial capital in Chapter 8, a quantitative way (investment
assets from the rich uncle may mean appraisal) will be used to bring this framework
ambivalent outcomes – a ridger good for into an economic analysis. But for the moment,
preventing land degradation, but further semi-quantitative and non-quantitative use of
demands in needing oxen in a timely fashion. indicators provide a useful means of gaining a
These demands potentially exacerbate land full impression of the land degradation
degradation when they cannot be met – in this situation.
case by convincing the neighbour to let him
have ploughing done first. It is important that
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